title: Penicillin susceptibility testing of gonococci by disc diffusion.
abstract: This study investigated the use of various beta-lactam discs in the detection of penicillin sensitive, intermediate resistant and resistant strains (minimal inhibitory concentrations of penicillin G of less than 0.06, 0.06 to 0.25, and greater than 0.25 mg/l respectively). Discs containing 0.15 and 0.6 microgram of penicillin G, and 5 microgram of methicillin were the most useful in separating the three groups. Cut-off zones between sensitive, intermediate resistant and resistant strains are 12 and 24 mm for 0.15 microgram penicillin discs; 24 and 32 mm for 0.6 microgram penicillin discs; and 20 and 30 mm for 5 microgram methicillin discs. Oxacillin discs (1 microgram) were useful in separating resistant from both sensitive and intermediate resistant strains at a cut-off zone of 8 mm. Use of a combination of discs provides the best index of susceptibility group, and at least two should be used
mesh_terms: D004305:Dose-Response Relationship, Drug; D008826:Microbial Sensitivity Tests; D009344:Neisseria gonorrhoeae / Q000187:drug effects* / Q000201:enzymology; D010400:Penicillin G / Q000494:pharmacology*; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: D001618:beta-Lactamases; D010400:Penicillin G